In U.S. Pat. No. 3,657,267 there are described a series of anthelmintic 5-acyl-(1H-benzimidazol-2-yl)carbamates, the best known member of which is methyl(5-benzoyl-1H-benzimidazol-2-yl)carbamate, generically designated as mebendazole. The novel compounds of this invention differ from the foregoing essentially by the nature of the ketal substituent in the 5-position of the benzimidazole nucleus.